(1) Field of the Invention
This invention relates generally to the field of electric motors, and more specifically to reduced weight electric motors, such as inductive electric motors, in which the weight of the rotor has been reduced, and to the rotor so constructed to reduce the weight of such a motor.
(2) Description of the Prior Art
Reducing the weight of a rotor in some types of motors by reducing the amount of material therein is known. The advantages of such savings usually include a reduction in manufacturing cost of the motor. In the past, many of the advances made in reducing the weights of laminations in rotors have been developed for DC motors. However, many of the applications in which reduced-weight motors would be useful, such as washing machines, employ induction motors, to which the improvements developed for DC motors either do not apply or would be impractical to apply.
Recent developments have been set forth for reducing the weight of rotors in induction motors, but these weight reductions required that the rotors be redesigned, resulting in a smaller motor of different dimensions than the original. Thus, a manufacturer of such a motor would have to retool his manufacturing operation to accommodate the smaller-size rotor. Moreover, a manufacturer of a device, such as a washing machine, in which a standard motor is used may have to retool to accommodate a lower-weight motor having smaller external dimensions. The marketplace for improved lightweight motors may also be reduced if an existing consumer appliance needing repair cannot accommodate a smaller, reduced weight motor, and consumer hostility may be created if the cost of a repair is increased because a replacement motor requires an extra-cost adaptor.
There are also some applications of induction motors in which an axial imbalance (such as that created by attachment of the motor to a crank, as in a reciprocating compressor) must be counterbalanced. Presently, this counterbalance is created by the axially asymmetric addition of extra weight 102 on one, or perhaps both shorting end rings 100 of a motor, as shown in prior art FIG. 9A and 9B, or by the addition of counterweights external to the motor, since the prior art has taught that the rotor of a motor should be made as symmetrical as possible. Adding additional material in the form of counterbalancing weights adds to the cost of the motor or motor assembly. There has thus been a long-felt felt need to provide a reduced-weight, and thus reduced cost motor for such applications, and a method for reducing the weight and cost of such motors.
It would thus be advantageous to provide a rotor for an induction motor that can be practically constructed with existing manufacturing equipment, but which provides a substantial reduction in weight through reduction in lamination material. It would further be advantageous if the reduction in weight was not accompanied by a reduction in size, so that a replacement motor made with such a rotor could maintain the same external dimensions as the motor being replaced.
It would also be advantageous to provide a rotor for an induction motor, and a method of manufacturing such a rotor, that would permit the motor to be used in applications in which an axial asymmetry must be counterbalanced, without adding or attaching significant additional weight to the motor.